The present disclosure is directed to an electrical connector which extends through a bulk head, and more particularly one which is provided with a protective rubber boot seal there-around on the high pressure side. It is a type of construction particularly useful in downhole logging tools. The circumstances in which this device is used are extremely difficult. Generally speaking, an electrical connector of this sort is intended to be used at elevated pressures and temperatures. It is not uncommon to lower a well tool into a well (both cased or open hole) where the operating pressure at several thousand feet down the well can be as high as 25,000 psi and the ambient temperature can be as high as 500.degree. F. Normally, such logging operations are carried out in the well borehole where the ambient environment is any of a mixture of liquid such as brine, oil based drilling fluids, and produced oil or natural gas. Natural gas typically carries highly reactive chemicals with it including methane, CO.sub.2 and H.sub.2 S. All of these materials form a prevailing atmosphere of reactive chemicals, and they are especially reactive at the elevated pressures and temperatures observed. The highly reactive chemicals in the fluids around such an oil well logging tool pose a serious problem in the construction of electrical feedthroughs.
In one application, this device is a feedthrough which is adapted to be placed in a bulk head where one side is exposed to a hermetically sealed chamber within the tool. The internal pressure may be reduced, perhaps even to atmospheric pressure creating a pressure difference up to 25,000 psi across the bulkhead. The internal chamber may be isolated by the hermetic construction of the case or housing which encloses the components. This case or housing is typically described as a sonde which encloses the requisite components; typically however the logging tool takes on the temperature of the surrounding fluid in the well and will increase in temperature to that prevailing temperature, even as high as 500.degree. F. Moreover, the exposed side of the feedthrough may well be exposed to the fluid which carries the various reactive constituents in it and is almost always conductive. Accordingly, highly corrosive reactions may attack the exposed side of the feedthrough. Just as one example, H.sub.2 S in the produced well fluid even in just a few parts per million (perhaps 1 to 10 ppm), provides a basis whereby hydrogen embrittlement may attack the metal case or housing made of steel. Special efforts have to be undertaken to isolate the steel housing from the highly reactive H.sub.2 S. Some materials which are successfully resistant to H.sub.2 S may however succumb to salt water, and especially salt water at such elevated pressures and temperatures. Indeed, the materials which are exposed to the feedthrough represent something of a witches brew in the ability of the materials to attack the surfaces of metals in the logging tool and especially at the feedthrough locations.
The present apparatus is a device having the form of an electrical feedthrough which is particularly effective to exclude the highly reactive fluids in the immediate vicinity of the feedthrough. The present apparatus includes a rubber boot which serves as an external seal to exclude reactive fluid constituents from contact against conductive elements of the feedthrough. Even so, the rubber boot poses a problem. At elevated pressure and temperatures, the rubber boot itself runs the risk of conversion of its resistivity. It is a very resistant material (electrically speaking) which is highly effective at temperatures prevailing at the surface of the well. At the elevated temperatures in a downhole situation, that does not hold true, and i t may become a type of unintended current bleed path from the interior to the exterior and providing current leakage which poses a problem. If the feedthrough is on a high current fitting such as one delivering system power for operation of the equipment within the sonde, the leakage current can be sizable. If a small electrical signal is transmitted through the feedthrough such as a signal in the range of a few millivolts, the leakage may be quite noisy and create problems in the quality of the signal transferred through the electrical connection. That also poses a problem. The present apparatus overcomes these problems by first arranging an externally located rubber boot seal which is incorporated to exclude the external fluids in the surrounding borehole. Moreover, electrical shorting as the rubber boot interacts with the prevailing fluids at the ambient temperature is avoided.